Braking system



Patented July 6, 1954 BRAKING SYSTEM John W. Holdeman, Detroit, Mich., assignor to Borg-Warner Corporation, Chicago, 111., a corporation of Illinois Application December 12, 1951, Serial No. 261,225

Claims.

My invention relates to transmissions for automotive vehicles having hydrodynamic torque transmitting devices therein which transmit ,torque at engine idling speeds as well as at greater speeds of the vehicle engine, and more particularly my invention relates to braking means for counteracting the tendency of the vehicle to creep or move slowly clue to the torque transmitted .through the hydrodynamic device at engine idling speeds.

Automotive vehicles are quite usually equipped with transmissions comprising such hydrodynamic coupling devices, which may take the form of hydraulic torque converters, the speed and torque output of which is dependent on the speed and torque applied to the Coupling device from the engine of the vehicles. A power train including such a hydrodynamic device may be maintained completed through the transmission for all forward driving; however, it has been found that the torque transmitted by the hydrodynamic device with the engine idling, under some conditions, such as when the lubricated parts of the vehicle are warm and therefore move easily, is sufiicient to cause the vehicle'to move slowly, so that with ordinary installations of this character, it is necessary for the vehicle operator to keep the vehicle. wheel brakes applied for preventing creepingof the vehicle due to the torque transmitted through the hydrodynamic device underengine idling conditions. 1 It is an object of the present invention to provide an improved system which overcomes the tendency of the vehicle to creep under engine idling conditions and prevents any torque being I applied'to the output shaft of the transmission'at gengine idling speeds. .commonly include planetary gearing and brakes Automotive transmissions the driven shaft of the transmissionunder engine idling conditions.

'Such'transmissions may comprise a brake cooperating with planetary gearing to provide a forward drive through the transmission'when'the brake is engaged and a brake cooperating with planetary gearing for providing a reversedrive through the transmission when the latter brake is engaged, and it is an object to provide a system which automatically engages both of the brakes for thereby preventing torque application from the hydrodynamic device to the output shaft of the transmission under vehicle engine idling conditions, such application of the brakes being under the control of a vehicle speed responsive means so that this application of both brakes is obtained only when the vehicle is traveling below a predetermined low speed.

Such power train completing brakes may comprise bands engageable on drums by means of fluid pressure actuated pistons acting on one end of the band and in such a direction as to increase the wrapping effect of the brake band for the direction of reaction on the brake drum for completing the respective power train from the drive shaft to the driven shaft of the transmission. It is an object of the invention to provide a second fluid pressure actuated piston operating on the other end of the reverse drive brake band, so that the direction of reaction on the brake drum for completing the reverse drive power train is in a direction opposing the action of the latter piston for thereby reducing the braking effect on the reverse brake drum whereby theeffect of the latter piston is easil overcome when the throttle of the vehicle engine is opened to start the vehicle in forward travel. It is also an object to make the latter piston with less area for application of vfluid pressure thereto to provide a smaller force than the piston for completing the reverse drive power train from the drive shaft of the transmission to the driven shaft.

The invention consists of the novel constructions, arrangements and devices to be hereinafter described and claimed for carrying out the above stated objects and such other objects as will appear from the following description of a preferred embodiment of the invention, illustrated --with reference to the accompanying drawing, 'wherein:

Fig. 1 is a schematic illustration of a transmission and a controlling system for the transmission embodying the principles of the invention; and

Figs. 2, 3 and 4 are sectional views taken respectively on lines 22, 3-3 and 44 of Fig. 1.

The invention constitutes an improvement on the vehicle braking systems disclosed in an application by JohnB. Polomski, Serial No. 230,489,

filed June 8, 1951,'and in applications by Warner G. Baule,- Serial No. 249,335, filed October 2, 1951, and Serial 'No. 256,490, filed November 15,- ,1951. Like characters of reference designate like parts in the several views. Referring now to the drawing, the transmission illustrated comprises a drive shaft [0 and a driven "shaft H. The drive shaft I0 is adapted tobe 3 driven by the engine I2 of the vehicle in which the transmission is installed, and the driven shaft II is adapted to drive the rear road wheels I3 of the vehicle through any suitable drive connections.

The transmission comprises in general a hydraulic torque converter I4, a planetary gear set I5, a second planetary gear set IS, a forward drive brake I1, a low speed lockup brake I8, a reverse brake I9, a highspeed forward drive clutch 20 and an intermediate speed clutch 2 I.

The hydraulic torque converter I4 comprises a bladed impeller 22, a bladed runner or driven element 23 and a bladed stator or reaction element 24. The impeller is connected to be driven from the drive shaft Ill. The stator 24 is connected with a one-way brake 25 which is effective for holding the stator 24 against rotation in the reverse direction, that is, in the direction of rotation opposite to that of the drive shaft I0. The brake 25 may be of any suitable construction and may, for example, comprise tiltable sprags 26 disposed between and engageable with inner and outer cylindrical raceways 21 and 28 as shown in Fig. 2.

The planetary gear set I5 comprises a ring gear 29, a sun gear 36, a plurality of planet gears 3| in mesh with the sun and ring gears and a planet gear carrier 32 for the planet gears 3|. The second planetary gear set I6 comprises a ring gear 33, a sun gear 34, a plurality of planet gears 35 in mesh with the sun and ring gears and a planet gear carrier 36. The ring gear 29 of the first planetary gear set is connected to be driven by the runner 23 of the torque converter I4, and the planet gear carrier 32 of this gear set is connected with the ring gear 33 of the secnd planetary gear set I6. The planet gear carrier 36 of the second gear set is connected with the driven shaft II.

The friction brake II comprises a brake band 3. engageable with a drum 38, and the brake I! is effective through a one-way brake 39 for braking the sun gear 34 and is effective through a second one-way brake 40 as well as the first one-way brake 39 disposed in series with the brake 46 for braking the sun gear 36. The oneway brakes 39 and 40 may be of any suitable well-known construction and may be of the sprag type similar to the brake 25. The one-way brake 39 comprises sprags 4| engageable with inner and outer cylindrical surfaces 42 and 43, and the brake 40 comprises sprags 44 engageable between inner and outer cylindrical races 45 and 45. Looking in the same direction at the brakes 39 and 46, the sprags of the two brakes are disposed in opposite directions between the inner and outer races as is apparent from Figs. 3 and 4.

The brake I8 comprises a brake band 4'! engageable on a brake drum 48 for augmenting the braking action of the one-way brakes 39 and 46 and the friction brake IT on the sun gear 30. The friction clutch 2| comprises discs 49 rotatable with the planet gear carrier 32, discs rotatable with the sun gear 30, opposite pressure plates 5| and 52, and a fluid pressure actuated piston 53 for moving the plate 52 toward the plate 5| to frictionally engage the two sets of friction discs with each other for engaging the clutch 2 I.

The reverse brake I9 comprises a brake band 54 engageable with a brake drum 55 connected with the carrier 32 of the planetary gear set I5 and with the ring gear 33 of the planetary gear set I6. The clutch 20 comprises a clutch disc 56 connected with the driven shaft I I and an axially movable pressure plate 51 having a fluid pressure actuated piston portion 58 and an axially stationary pressure plate 59 both rotatable with the drive shaft I0 and between which the disc 56 is engaged.

Each of the brakes I'|, |8and I9 is engaged by a fluid pressure actuated servomotor, the brakes I1, I8 and I9 being respectively engaged by servomotors 66, 6| and 62. The servomotor 66 comprises a fluid pressure actuated piston 63 for engaging the brake band 3'! on the drum 38; the servomotor 6| comprises fluid pressure actuated pistons 64 and 65 for engaging the brake band 41 on the drum 48; and the servomotor 62 comprises pistons 66 and 61 for engaging the brake band 54 on the drum 55. Return springs 68, 69 and 10 are provided in the motors 60, 6| and 62 respectively for disengaging the bands from the drums.

One end of the reverse brake band 54 is acted on by the pistons 66 and 61 as is shown and has been described, and the opposite end of the band 54 is held from movement, when the pistons 66 and 61 are effective to engage the brake band 54 on the drum 55, by means of a piston II slidably disposed in a cavity I2 formed in a casing portion I3. An anchor screw I4 is provided in the casing portion I3 limiting movement of the piston II.

In operation, the transmission provides low, intermediate and direct forward speed drives and a drive in reverse. The transmission, when the clutches 20 and 2| and the brakes I'I, I8 and I9 are all disengaged, is in a neutral condition, and the shaft I I is not driven from the shaft II) when the latter is rotated by the engine I2. The low speed forward drive may be completed by engaging the brakes 'I'! and I8. The sun gear 34 is braked by means of the friction brake I1 and the one-way brake 39 from rotation, and the sun gear 30 is braked by the friction brake I8 and the one-way brake 40 from the sun gear 34. The runner 23 in the torque converter I4 is driven through the medium of the fluid in the torque converter from the impeller 22 and the drive shaft I6, and the runner 23 drives the ring gear 29 of the gear set I5. The sun gear 36 of this gear set is braked to be stationary, as has just been described, and the planet'gears 3| planetate between the sun gear 30 and ring gear 29 to drive the carrier 32 at a reduced speed and increased torque in the forward direction. The ring gear 33 of the second planetary gear set I6 is connected with the carrier 32 and is driven thereby. The sun gear 34 of the gear set I6 is braked to be stationary, as has just been described, and the planet gears 35 of this gear set planetate between the ring gear 33 and the sun gear 34 and drive the planet gear carrier 36, which is connected with the driven shaft II, at a further reduced speed and increased torque in the forward direction. The driven shaft I I is thus driven at an increased torque with respect to that impressed on the drive shaft II), an increase in torque taking place in each of the units consisting of the hydraulic torque converter I4, the planetary gear set I5 and the planetary gear set I6.

Intermediate speed forward drive through the transmission is completed by disengaging the brake I8 and engaging the clutch 2 I. The clutch 2| connects together the planet gear carrier 32 and the sun gear 30 of the planetary gear set I5 'therebylocking up the gear set and causing all of its elementsto rotate together as a unit. The ring gear 33 of the second planetary gear set I6 is thereby driven from the runner 23 at the same speed as the runner, and the speed of the driven shaft II is thereby increased with respect to its speed in low speed forward drive.

Direct drive through the transmission is completed by engaging the clutch 20 which directly connects together the drive shaft I with the driven shaft II. Both the clutch 2I and the brake I1 may be allowed to remain in engaged condition for this drive.

;Reverse drive is completed through the transmission by engaging the reverse brake I9. The brake I9 functions to hold stationary the planet gear carrier 32 of the gear set I5 and the ring gear 33 of the gear set I6 connected with the carrier 32. The ring gear 29 is driven as in the forward drives through the hydraulic torque converter I4 from the drive shaft I0, and the sun gear 30 is driven at an increased speed in the reverse direction through the intermediary of the planet gear pinions 3| held against planetary rotation about the centers of the shafts I0 and II by the brake I9. The sun gear 30 drives the sun gear 34 of the planetary gear set I6 through the one-way brake 40 which now functions as a clutch. The ring gear 33 of the gear set I6 being held stationary by the reverse brake I9 functions as the reaction element of the gear set I6 to cause a drive of the planet gear carrier 36 and thereby the driven shaft I I in the reverse direction at a speed which is reduced below the speed of the sun gear 30 due to the action of the planet gear pinions 35 rotating within the ring gear 33.

The reaction on the drum 55 for the reverse drive power train, with the power being transmitted from the drive shaft I0 to the driven shaft II, is in the direction indicated by the function to move the end 54b of the band 54 in the same direction that the reaction force on the drum 55 tends to move this end of the band when it frictionally contacts the drum 55, and the band 54 thus has a wrapping or self-energizing effect for this direction of reaction.

The control mechanism for the transmission comprises in general a pump 80 driven by the drive shaft I0 of the transmission, a pump 8| driven by the driven shaft I I of the transmission, a manual selector valve 82, a direct drive shift valve 83, a front pump relief valve 84, and a rear pump relief valve 85.

The drive shaft pump 80 comprises an inner gear 86 driven through the intermediary of the impeller 22 of the torque converter I4 from the drive shaft I0 and an outer gear 81 eccentrically located with respect to the inner gear 86 and in mesh with the latter gear. A crescent shaped casing portion 88 separates the gears 86 and 81,

as shown. The pump 80 is connected with an inlet conduit 89 and thereby with a fluid sump 90, and the pump is also connected with an outlet conduit 9I. The pump is of. a well-known construction and operates as is well understood' outer gear 81 rotates in the same direction due to its meshing engagement with the gear 86, the pumping action being due to the fluid carried by the gears 86 and 81 across the inner and outer faces of the crescent shaped casing portion 86.

The driven shaft pump 8| comprises a gear 92 driven by the driven shaft II in mesh with a gear 93. The pump 8| is connected with an inlet conduit 94 which is connected to draw fluid out of the sump 90, and the pump is connected with an outlet conduit 95. The pump 8| also is of wellknown construction and operation, carrying fluid between its gear teeth to provide its pumping action.

The outlet conduit 9| of the drive shaft pump is connected with the rear pump relief valve 85, as shown. The valve comprises a piston 96 slidably disposed in a casing portion 91. The piston 96 has lands 98 and 99 and a groove I00 between the lands. The casing portion 91 is provided with a port IOI, two connected ports I02, a port I03 and a port I04, as shown, and it has connected cavities I05 and I06 of respectively larger and smaller diameters in which the lands 98 and 99 are respectively slidable. A compression spring I01 is provided between the lower end of the piston 96 and the lower'end of the cavity I05.

is connected by means of a branch conduit I09 with the ports I82 and the outlet conduit 9| for the pump 80. A check valve IIO comprising a ball II I adapted to rest on a seat I I2 is provided in the conduit I99 for allowing fluid to flow through the conduit in only one direction. The ports IOI and I03 of the valve 85 are bleed ports adapted to freely discharge fluid into the sump 90.

The front-pump relief valve 84 is connected with the conduit I09, as shown, and comprises a piston II3 slidably disposed in a casing portion H4. The valve piston I I3 comprises land I I5 and II 8 and a groove II1 between the lands. The casing portion II4 has ports II8 and II 9 as shown, the port I I9 being a bleed port for freely discharging fluid into the sump 99. The casing portion I'I4 has cavities I20 and I2I of respectively smaller and larger diameters in which the lands II5 and H6 are respectively slidable, and the cavity I2I at its upper end is connected to the conduit I09. A spring I22 is provided between the land H6 and the upper edge of the cavity I20.

The outletconduit for the pump 8| is connected with the port I 04 in the valve 85, and this conduit is also connected with the regulated pressure conduit I08 by means of a branch conduit I23. A. check valve I24 is provided in the conduit I23 and comprises a ball I25 adapted to rest on a seat I26.

The regulated fluid pressure conduit I 08 is connected with the manual selector valve 82. The valve 82 comprises a valve piston I21 slidably disposed in a casing portion I28. The piston I21 is provided with lands I29, I30, I3I and I32 and grooves I33, I34 and. I35 between the lands. The casing portion is provided with ports I35, I31, I38, I39, I40, MI, I42 and I43. The port MI is a bleed port through which fiuid may freely discharge into the sump 90, and the port I31 is connected with the regulated fluid pressure conduit I08. The port I40 is connected by means of a conduit I44 with the brake servomotor 6| for applying fluid pressure at times to the pistons 64 and 65. The ports I39 and I42 are connected A regulated fluid pressure supply conduit I98 by means of a conduit I45 with the brake servomotor 68 for applying pressure at times to the piston 53, and the port I43 is connected by means of a conduit I46 with the brake servomotor 62 for applying pressure to the pistons 66 and 61. The port I36 is connected to the port II 8 in the front pump relief valve 84 by means of a conduit I41.

The port I38 in the selector valve 82 is connected by means of a conduit I48 with the direct drive shift valve 83. The valve 83 comprises a valve piston I49 slidably disposed in a casing portion I513. The piston I49 is provided with lands II, I52 and I53 and grooves I54 and I55 between the lands. The casing portion I50 is provided with ports I56, I51, I58, and I59. The port I59 is a bleed port adapted to freely discharge fluid into the sump 90; the port I55 is connected with the conduit I48; the port I5! is connected by means of a conduit I58 with the pressure piston 53 of the friction clutch 2I; and the port I58 is connected by means of a conduit IEiI with the pressure plate piston portion 58 of the friction clutch 20. The piston I49 of the direct drive shift valve may be moved manually or by any suitable automatic means (not shown) A restricted drain passage I62 is connected with the discharge conduit 95 for the driven shaft pump SI. A check valve I 63 is disposed between the restricted passage I62 and the discharge conduit 95 and comprises a ball I64 adapted to rest on a seat I65 and yieldably held thereon by means of a spring I55.

The engine I2 for the automotive vehicle is controlled in accordance with usual practice by means of an accelerator E51 which is connected with the throttle lever I58 of the engine carburetor I69.

The operation of the transmission and its controls as so far described is as follows: The transmission is conditioned for various types of operation by moving the manually operated selector valve piston I21 into any of its various positions which are the N or neutral position, the D or drive range position, the L or low range position and the R, or reverse drive position, all of which are indicated in the drawing. When the valve piston I21 is in its N or neutral position, there is no drive between the shafts I5 and II. It is assumed that the vehicle engine I2 is in operation, and the pump 85 which is driven through the impeller 22 from the drive shaft I9 draws fluid from the sump 55 through the conduit as and discharges it into the conduit SI. It flows between the opposite ports I52 in the valve 35 and through the conduit I59 into the regulated fluid pressure supply conduit I58.

The check valve H5 is opened by the fluid from the pump 35 with the ball HI being moved oil the seat II2 to provide communication through the conduit I69 to the conduit I523. The pressure in the conduits I69 and its is maintained at a predetermined maximum by means of the front pump relief valve 84. The pressure in the conduit IE9 is impressed on the upper end of the valve piston H3 and moves the valve piston H3 into substantially its illustrated port cracking position in which the land I I5 allows fluid from the conduit I09 to flow through the bleed port H9 and thereby to the sump 95, this movement of the valve piston II3 into port cracking position being against the action of the spring I22. As will be apparent, a decrease in fluid pressure in th conduit I59 will allow the piston II3 to move upwardly under the influence of the spring mum pressure.

selector valve piston I21, however the land I29 them. The driven shaft and the driven shaft II 8 I 22 to decrease the port crackingeffect of the land H6, and an increase in the fluid pressure in the conduit I59 functions to move the valve piston II3 farther downwardly against the action of the spring I22 to increase the port cracking eifect of the land IIB, so that the net effect of the valve -84 is to maintain the fluid in the conduits I09'and IE8 at a predetermined maxi- In the neutral position of the of this piston blocks the port I31 for the conduit I08, so that this fluid pressure does not pass through the selector valve 82 to any of the brakes or clutches in the transmission for engaging II is assumed to be stationary, and the pump 8| therefore provides no output fluid pressure in its conduit 95.

Ordinary forward driving by means of the illustrated transmission is'done in drive range, in which the selector valve piston I21 is in its D position. In this position of the piston I21, driving is initially through the intermediate speed power train, and a change in speed ratio to high speed drive may be subsequently obtained by moving the direct drive shift valve piston I49 out of its illustrated position, either manually or by any suitable automatic valve shifting means (not shown). In the D position of the selec tor valve piston I21, regulated pump pressure from the conduit I08 is conducted by means of the groove I33 and ports I31 and I38 to the conduit I48, and fluid under pressure also flows through the groove I53 and port I42 to the conduit M5. The conduit I45 is connected with the servomotor for the forward drive brake I1, and the brake I1 is thus applied by application of fluid pressure to the servo piston 63. The fluid pressure in the conduit I48 flows through the port I55 in the direct drive shift valve 83 and through the groove I54 and port I51 into the conduit I55 connected with the clutch piston 53 so that the clutch 2! is also engaged. Engagement of both the clutch 2I and the brake I1 completes the intermediate speed power train, and the vehicle are started and are subsequently driven at increasing speeds by depressing the accelerator I51 and thereby increasing the power delivered from the engine I2.

The driven shaft pump 8|, as the driven shaft H begins rotation and increases in speed, delivers fiuid to its discharge conduit -95 and draws fluid from the sump 55 through its inlet con duit's i. The fluid pressure in the conduit 95 is impressed on the upper end of the valve piston 55 of the rear pump relief valve 85 through the conduit I25 and tends to move the valve piston 53 downwardly. against the action of the spring H71. When the pressure in the conduit 95 has increased sumciently, such movement of the piston 55 takes place, so that the land as of the piston 96 moves out of the cavity 556 to provide a cracking or small opening between the lower edge Itfia of the cavity I05 and the upper edge '85 to reduce the fluid bleed to the sump through the port I 03 and tending to open farther with any increase in pressure in the conduit 95 to increase the bleed to the sump. The valve piston 96, when so moved to vent the port I94 to and materially reduce the amount of power required for driving the pump 80. Under'these conditions, with the driven shaft pump 8| supplying substantial fluid under pressure, the check valve I25 is opened by the fluid pressure in the conduits 95 and I23, with the ball I25 moving off its seat I26, and-the regulated pressure in the conduits I23 and I08 is supplied by the driven shaft pump 8I, exclusive of the drive shaft pump 80. Since the output conduit 9| of the drive shaft pump 80 is connected by means of the valve 85 with the bleed port I03, there is no fluid under pressure in the portionof the conduit I09 between the check valve I I and the valve 85 tending to hold the check valve IIO open, and the check valve I I0 closes with its ball moving on to the seat I I2 to prevent any of the fluid in the conduit I08 draining through the groove I00 in the valve 85 and the bleed port I03 to the sump 90.

A change from second or intermediate speed drive to third speed drive is obtained by shifting the valve piston I49- from its illustrated position into a position connecting all three ports I56, I51 and I58. The valve piston may be so shifted either automatically or manually, as desired. In the changed position of the valve piston, the groove I54 of the piston provides communication between the conduit I48 containing regulated fluid pressure and the conduit ISI for ,piston I21 into its L position in which the groove I33 connects the ports I31 and I42 and the groove I35 connects the ports I39 and I40. The regulated fluid pressure in the conduit I08 is supplied through the port I31, the groove I33 and the port I42 to the conduit I45 and the forward brake servomotor 60, and the brake I1 is thus applied. The fluid pressure in the conduit I45 also passes through the port I39, the groove I35, the port I40 and the conduit I44 to the low brake servomotor 6|, and the brake I8 is aplied by the fluid pressure on the servomotor pistons 64 and 65. With these two br'akes'engaged, as has been previously explained, the low speed power train through the transmission is completed. The drive shaft pump 80 produces the fluid under pressure in the'flu'id supply conduit I08 for engaging the brakes I1 and I8 and keeping them engaged until the driven shaft pump 8I increases to a substantial speed, the same as when the vehicle is started and driven in interthus supplied to the conduits I41 and I46. For

reverse drive, the fluid pressure in the conduit I08 is obtained from the drive shaft pump 60 exclusive of the driven shaft pump 8I, since the latter pump rotates in the reverse direction and does not supply fluid to its outlet conduit 95. The fluid from the pump flows through the conduits 9| and I 09 to the fluid pressure supply conduit I08 as in intermediate forward drive, for example, and the front pump relief valve 84 is effective for limiting the pressure in these conduits to a predetermined maximum.

The fluid pressure in the conduit I41 connected with the conduit I08 by means of the valve piston I2'I is supplied to the piston groove H1 in the valve 84 through the port I I8, and the fluid pressure in this groove is effective to augment the action of the spring I22 and tend to move the valve piston I I3 upwardly to'decrease the amount of fluid flow between the upper end of the piston I I 3 and the edge of the port I I9. The fluid pressure in the groove II! is effective to supply this force to the piston II3 since the land end 611 is larger than the land end I I 5a asshown. The effect of this force on the front pump relief valve piston I I3 is to increase the pressure in the conduit I09 and in the connected conduits to a pressure which is substantially greater than that existing in the conduit I09 and connected conduits without any such fluid pressure being supplied to the groove II! of the piston II3, as in intermediate forward drive, for example. The reverse brake I9- is applied by fluid pressure from the conduit I46 which is connected with the conduits I08 and I09 by means of the ports I43 and I3! and the piston groove I33, and this increased pressure is supplied to the reverse brake servomotor 62 and particularly to the pistons 66 and 61 in this servomotor for applying the reverse brake I9 with a braking force which is greater than would otherwise be obtained with the fluid pressure regulated to a lower value as is used for the forward speed drives. An engagement of the brake I9, as has been previously described, completes the reverse drive power train through the transmission, and the increased force of application on the brake I9 due to the increased fluid pressure functions to prevent slippage of the brake I9 due to the reaction on the brake which is greater than the reactions on the other brakes for the forward speed drives. The application of force by means of the pistons 66 and 61 to the particular end 5417 of the brake band 54, tending to cause the band to wrap on the drum 55- due to the direction of reaction on the drum for the forward drive,'also augments the braking action of the band54.

The restricted passage I62 connected with the discharge conduit 95 of the driven shaft pump 8| has the function of relieving trapped fluid in the conduit 95 after movement of the driven shaft I I for forward drives of the vehicle has ceased. The check valve I63 will remain open with its ball I64 being off the seat I65 until the fluid pressure in the conduit 95 has decreased to an insubstantial value after the pump 8| has ceased operation from forward rotation of the shaft I I. Any fluid pressure in the conduit 95 which would tend to maintain the piston 96 of the rear pump relief valve in a position relieving fluid pressure in the discharge conduit 9I of the drive shaft pump 80 is thus removed, instead of being trapped in a closed system when the vehicle is stationary.

The output torque delivered by the hydraulic torque converter I4 to the ring gear 29 of the planetary gear set I5 is dependent on the speed of the impeller 22 and the engine I2 driving the torque converter. The output torque of the converter I4 increases gradually as the speed of the engine and impeller 22 increases, and when the engine I2 is running at idling speed and either the low speed forward power train or the intermediate power train is completed, the torque transmitted by the converter I4 supplies sumcient torque to the driven shaft II so that generally the vehicle creeps or moves slowly unless it is in some way restrained. According to my invention, I provide improved mechanism for restraining the rotation of the driven shaft I I when the vehicle engine I2 is idling so as to overcome this tendency of the vehicle to creep whereby the vehicle operator may maintain either the intermediate or low speed power trains completed, preliminary to starting the vehicle moving by opening the engine throttle without the necessity of braking the vehicle by means of the road wheel brakes.

The vehicle anti-creep mechanism of my invention comprises a valve I80 connected by means of a conduit I8I with the forward drive brake conduit I45, connected by means of a conduit I82 with the cavity I2 for the application of fluid pressure to the piston II and connected by means of a conduit I83 with the discharge conduit 95 of the driven shaft pump 8 I. The valve I80 comprises a valve piston I84 slidably disposed within a cylindrical cavity I85 formed within a casing portion I85. The piston I84 is formed with lands I81 and I88 and has a groove I89 between the lands. The casing portion I88 is provided with ports I90, IBI, I92 and I93, and the ports I90, I9I and I92 are respectively connected with the conduits IBI, I89 and I82. The port I93 is a bleed port adapted to freely discharge fluid into the sump 90. A compression spring I94 is provided between the piston I84 and an end of the cavity I85, as shown.

In operation, the reverse brake band 54 is applied on the drum 55 whenever the vehicle is stationary and the transmission is conditioned for either its intermediate or low speed forward drives in which the vehicle is generally started from rest. As has been explained, the selector valve piston I2? is moved into its D" position in which it is illustrated or into its L position for conditioning the transmission for these drives,

and fluid pressure exists in the conduit I45. The valve ISO is vehicle speed responsive, as will be described, and is in its illustrated position when the vehicle is at rest. Fluid pressure is applied through the conduit I8I connected with the conduit I45, the port I90, the groove I89 of the piston I84, the port I92 and the conduit I82 to the piston II. This application of fluid pressure to the piston II causes application of the reverse brake band 54 on the drum 55, and both the brake I! and the band 54, as well as the brake IS in low range drive, are thus engaged. Both forward drive and reverse drive power trains are thus simultaneously completed resulting in a locking up of the transmission, so that the runner 23 and all of the elements of the two gear sets I5 and I5 are locked and cannot rotate, and the driven shaft II is thus also locked. No power is thus transmitted through the transmission to cause any movement of the vehicle, and the vehicle operator need not therefore resort to use of the vehicle brakes for preventing creeping movement of the vehicle under engine idling conditions.

It will be noted, however, that the application of thereverse brake band 54 on the drum 55 is with less intensity than would be the case if the pistons 56 and 51 were used as for reverse drive, not only due to the fact that the pistons 56 and 5? are larger and present an over-all greater surface to which fluid pressure is applied as compared with the piston II but in addition, the reduced fluid pressure in the conduit I is utilized as compared with that present in the conduit I46 when the transmission mechanism is conditioned for, its reverse drive by a positioning of the selector valve piston I2I in its R, position. Furthermore, the use of the piston II acting. on the end 54a of the band 54 causes an unwrapping effect with respect to the direction of reaction on the drum indicated by the arrow I5 for completing the reverse drive power train from the drive shaft I0 to the driven shaft II.

The reverse brake band 54 applied to the drum 55 by the piston II is disengaged when the speed of the vehicle reaches a predetermined low value, such as for example 3 or 4 miles per hour. At this speed, the driven shaft pump 8| develops suflicient output pressure in the conduits 95 and I83, which is applied through the port I9I on the right end of the piston I84, to move the piston I84 to the left against the action of the spring I94, so as to connect the ports I92 and I93 to drain fluid from the cavity I2 and the conduit I82 and to block the conduit IBI and the port I connected with the driven shaft pump 8 I. The initial move- .ment of the vehicle is against the braking action of the piston II on the band 54; however, due to the fact that the piston II is effective only to apply the band 54 on the drum 55 with a relatively low pressure for the reasons above mentioned the band 54 slips on the drum 55 upon the vehicle being driven initially, below the vehicle speed at which the valve I84 is shifted. It is contemplated that the engaging force supplied by the piston II to the band 54 is only sufficient to prevent a creep of the vehicle under engine idling conditions and causes little impedance to movement of the driven shaft I I in the forward direction through either the lowe or intermediate speed power trains when the vehicle engine speed is increased.

My improved vehicle anti-creep braking system advantageously causes a braking of the vehicle when the transmission of the vehicle is conditioned for a start in a forward drive whereby the hydraulic torque converter of the transmission is not then effective to drive the vehicle. The anti-creep system causes an automatic discontinuance of the braking effect when the vehicle has substantial forward motion, and the braking effect on the reverse brake I9 is substantially less than that on the forward brake I1 so that when the vehicle accelerator is depressed for starting the vehicle, the reverse brake band 54 slips easily and provides little impedance to the forward motion of the vehicle.

I wish it to be understood that my invention is not to be limited to the specific constructions and arrangements shown and described, except only insofar as the claims may be so limited, as it will be understood to those skilled in the art that changes may be made without departing from the principles of the invention.

I claim:

1. In transmission mechanism for an automotive vehicle having a dIiVll'lg engine, the combination of a drive shaft adapted to be driven by the vehicle engine, a driven shaft adapted to drive the vehicle, a hydrodynamic coupling de- 13 vice driven by said drive shaft, means for completing a first power train between said hydrodynamic device and said driven shaft for driving said driven shaft and the vehicle, means for completing a second different power train between said hydrodynamic device and said driven shaft for driving said driven shaft and the vehicle and including a brake band engageable by fluid pressure actuated piston means on a brake drum for completing the latter power train when engaged, and means for temporarily holding said driven shaft from rotation due to torque transmitted through said hydrodynamic device and said first power train and including a fluid pressure actuated piston effective to engage said brake band on said drum to complete said second power train simultaneously with said first power train, said piston havinga smaller area on which fluid pressure is applied for engaging said band than said piston means whereby the band slips on said drum to break said second power train when the power output of the vehicle engine is increased for driving said driven shaft through said first power train.

2. In transmission mechanism for an automotive vehicle having a driving engine, the combination of a drive shaft adapted to be driven by the vehicle engine, a driven shaft adapted to drive the vehicle, a hydrodynamic coupling device driven by said drive shaft, means for completin a first power train between said hydrodynamic device and said driven shaft for driving wrapped around the drum due to the reaction on the drum for the drive from the drive shaft to the driven shaft through said second power train whereby the piston means acts in a brake energizing direction, and means for temporarily holding said driven shaft from rotation due to torque transmitted through said hydrodynamic device and said first power train and including a fluid pressure actuated piston effective to engage said brakeband on said drum to complete I said second power train simultaneously with said first power train, said piston being effective on the other end of said band so that the band is unwrapping or self-deenergizing for the direction of reaction on'the drum for a drive from the drive shaft to the driven shaft through said second power train whereby the band slips on said drum to break said second power train when the power output of the vehicle engine is increased for driving said driven shaft through said first power train.

3. In transmission mechanism for an automotive vehicle having a driving engine, the combination of a drive shaft adapted to be driven by the vehicle engine, a driven shaft adapted to drive the vehicle, a hydrodynamic coupling device driven by said drive shaft, means for completing a first power train between said hydrodynamic device and said driven shaft for driving said driven shaft and the vehicle, means for completinga second difierent power train between said hydrodynamic device and said driven shaft for driving said driven shaft and the vehicle and including a brake band engageable by fluid pressure actuated piston means on a brake drum for completin the power train when engaged, said piston means being effective on one end of said band which tends to wrap around the drum due to the direction of reaction on the drum when the drive is from said drive shaft to said driven shaft through said second power train, and means for temporarily holding said driven shaft from rotation due to torque transmitted through said hydrodynamic device and said first power train and including a fluid pressure actuated piston efifective to engage said brake band on said drum to complete said second power train simultaneously with said first power train, said piston being effective on the other end of said band and having a smaller area than said piston means on which fluid pressure is applied for engaging said band whereby the band slips on said drum to break said second power train when the power output of the vehicle engine is increased for driving said driven shaft through said first power train.

4. In transmission mechanism for an automotive vehicle having a driving engine, the combination of a drive shaft adapted to be driven by the vehicle engine, a driven shaft adapted to drive the vehicle, a hydrodynamic coupling device driven by said drive shaft, means for completing a first power train between said hydrodynamic device and said driven shaft for driving said driven shaft and the vehicle, said means including a first friction band actuated by fluid pressure operated piston means for engaging a first brake drum to complete the power train, means for completing a second different power train between said hydrodynamic device and said driven shaft for driving said driven shaft and the vehicle and including a second brake band engageable by fluid pressure actuated piston means on a second brake drum for completing the second power train when engaged, and means for temporarily holding said driven shaft from rotation due to torque transmitted through said hydrodynamic device and said first power train and including a fluid pressure actuated piston effective to engage said second brake band on said second drum to complete said second power train simultaneously with said first power train, said piston having a smaller area on which fluid pressure is applied for engaging said second band than said piston means for either of said bands whereby said second band slips on said second drum to break said second power train when the power output of the vehicle engine is increased for driving said driven shaft through said first power train.

5. In transmission mechanism for an automotive vehicle having a driving engine, the combination of a drive shaft adapted to be driven by the vehicle engine, a driven shaft adapted to drive the vehicle, a hydrodynamic coupling device driven by said drive shaft, means for completing a forward drive power train between said hydrodynamic device and said driven shaft for driving said driven shaft and the vehicle, said means including a first brake band engageable by fluid pressure actuated piston means on a first brake drum for completing the power train when engaged, means for completing a reverse drive power train between said hydrodynamic device and said driven shaft for driving said driven shaft and the vehicle and including a second brake band engageable by fluid pressure actuated piston means on a second brake drum for completing the reverse drive power train when en- 15 gaged, means for temporarily holding said driven shaft from rotation due to torque transmitted through said hydrodynamic device and said forward drive power train and including a fluid pressure actuated piston effective to engage said second brake band on said second drum to complete said reverse drive power train simultaneousiy with said first forward power train, said piston means on said second band being applied on an end thereof which tends to wrap around said second drum for the direction of reaction on the drum for the reverse drive from said drive shaft to said driven shaft so that the brake band is self-energizing, said piston being eifective on the other end of said second brake band and said piston having a smaller area On which fluid v pressure is applied for engaging said second brake hand than said piston means for either of said bands whereby said second bandslips on said second drum to break said reverse power train when the power output of the vehicle engine is increased for driving said driven shaft through said forward drive power train, and means responsive to changes in rotation of said driven shaft for maintaining said piston inoperative and said second band disengaged from said second drum above a predetermined speed of said driven shaft in the forward direction. 1

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,541,391 Weiss Feb. 13, 1951 2,566,518 Farkas Sept. 4, 1951 2,599,215 Wemp June 3, 1952 FOREIGN PATENTS Number Country Date 966,238 France Oct. 4, 1950 

